# Calculations of Thiessen Polygon Bifurcated Areas

I have got a SewerGEMS network of a Sewerage Scheme for a Town. The Town is divided into 17 Wards having different Population Densities in (Population/Hectare). There is a AutoCAD drawing showing the Ward Boundaries with the Number for each Ward. I also have a separate Excel Sheet having the 2 Columns specifying Ward Numbers and Population Density for each Ward (Population/Hectare). I have generated the Thiessen Polygons for the 1476 Manholes in the Network specifying a Buffering Percentage only (i.e. No Separate Ward Boundary Used) . Now the issue is that many manholes will have areas of influence in 2 or more Wards with different Population Densities and thereby different flows.

How do I calculate the corresponding areas served by each manhole in different Wards?

Once I get these Bifurcated Areas I can multiply it by the Corresponding Population Density for the Corresponding Ward / Wards (If the area of influence is in 2 or more Wards) to get the Population Count for each manhole. I want to know the detailed process for getting these Areas of Influence of each manhole in Separate Wards i.e. the Bifurcated Thiessen Polygon Areas for each Manhole having Areas of Influence in 1 or 2 or more Wards having Different Population Densities..

• The best you're going to get is an estimation. Consider intersecting your manhole Thiessen with your wards (or union), calculating the intersecting area (calculate geometry), calculate the expected population based on the orignal ward density and then dissolve by Thiessen FID using Dissolve summing up calculated population. – Michael Stimson Nov 10 '14 at 22:42
• possible duplicate of Thiessen Ploygon Bifurcated Areas Calculations – Conor Nov 26 '14 at 15:17